In the present text, “foil bearing” designates a radial bearing or an axial thrust bearing including foils enabling a fluid film for levitation to be created, enabling the rotation of one component in relation to another by means of this fluid film, in particular a gas, and more specifically air. Such foil bearings are generally used for very high speeds of rotation and relatively low axial or radial loads in comparison with the loads supported by other types of bearing (ball bearings or hydrodynamic bearings, for example).
Such foil bearings (cf. for example FR 2 670 545, FR 2 700 821 etc.) are generally constituted by a first component on which elastic foils are fixed by an edge which is oriented orthogonally to the direction of rotation, the opposite edge of which extends, in the direction of rotation, in the direction of the second component, in order to realize, when the assembly is set in rotation, an “air wedge” enabling the levitation of the second component in relation to the first component to be ensured. Each foil is maintained at a distance from the first component by at least one corrugated stiffener interposed between the foil and said first component.
Such corrugated stiffeners are extremely sensitive components and have to display particularly elevated mechanical characteristics, notably a tensile strength greater than 1000 MPa, a 0.2% yield strength greater than 700 MPa, a minimum elongation greater than 20%, and a hardness (on the section) greater than 390 HV.
In order to display such characteristics combined with the presence of the corrugations, the known methods for producing these corrugated stiffeners are lengthy and costly. They consist in plastically deforming a plane sheet consisting of metallic superalloy with structural hardening (by precipitation) by stamping, in order to form the corrugations therein, then in winding the sheet corrugated in this way between two cylindrical rings in the form of a cylindrical solid of revolution, and in realizing a heat treatment for hardening said sheet (typically at more than 700° C. over a period of at least 20 h) to obtain the desired mechanical characteristics. U.S. Pat. No. 4,277,113 describes starting from a foil of annealed Inconel X-750, splitting and forming this foil in a die to obtain the corrugations, lining this foil afterwards with a layer of copper, and subjecting the assembly to a heat treatment at more than 700° C. for 20 hours, enabling a high resistance to the temperatures at the Inconel to be obtained, and obtaining the diffusion of the copper into the upper portion of the foil.
These known methods present various drawbacks. First of all, they impose manipulations, both of the corrugated sheet after stamping and also of the tools for heat treatment, which are lengthy, costly and particularly delicate, in order to avoid any untimely localized deformation of the shape of the corrugations obtained by stamping. In addition, the final heat treatment for structural hardening, which is necessary with a superalloy having structural hardening, is a costly and energy-consuming operation. These known methods cannot therefore be exploited on an industrial scale in mass-production applications, such as in the field of the manufacture of automobiles, for example.